What is the difference between append() and extend()?

append():

• Adds a single item to the end of the list.
• The item can be of any type (including another list).
• If you append a list, it adds the whole list as one element (nested list).

• a = [1, 2, 3]
  a.append([4, 5])
  # Result: [1, 2, 3, [4, 5]]

extend():

• Adds each element from an iterable (like a list, tuple, etc.) to the end of the list.
• It "extends" the list by adding elements one by one.
• If you extend with a list, its items are added individually (not nested).

• a = [1, 2, 3]
  a.extend([4, 5])
  # Result: [1, 2, 3, 4, 5]